Field of Invention and Prior Art
This application relates, in preferred embodiments, to recycling waste paper. Before waste paper can be reused, it is subject to pulping, deinking and bleaching processes. The cost of the waste paper and bleaching processes constitute a major part of the manufacturing cost for the production of paper products. Prior art methods controlled deinking and bleaching based upon the brightness of the incoming fiber with the attempt being made to deink and then bleach to a target brightness level.
Recycling is all the more difficult with respect to waste paper grades containing substantial amounts of groundwood fiber, also known as high lignin containing fiber. In recent years, waste paper costs have increased and the availability of low lignin waste paper has decreased. Thus, to continue economic operations of the large mills, the relatively plentiful high lignin containing waste paper and pulp feedstock has to be employed, especially with respect to economy or away-from-home tissue and towel products.
We have discovered a spectrophotometric and staining process which can be utilized in a short period of time, usually less than ten minutes in a commercial setting to enable us to evaluate what deinking and bleaching process to employ on the pulp. It should be noted that our process does not register colorless chemically treated fibers as groundwood. This is one shortcoming of the commonly used TAPPI Method T 236 om-99 for determining Kappa numbers. The TAPPI Method does not distinguish between untreated and treated lignin in fibers and therefore forces the use of excess chemical treatment for pulp which is suitable for the manufacture of absorbent paper products. This is particularly problematic since bleached-chemithermomechanical pulp (BCTMP) constitutes a significant part of the recycle fiber supply. The TAPPI Method also takes more than twice as long as the process claimed herein to determine the amount of groundwood in the pulp. The TAPPI Method is therefore impractical for use in large scale paper making operations.
Illustrating the state-of-the-art generally with respect to repulping, deinking and bleaching wastepaper-derived secondary furnish are U.S. Pat. No. RE36,424 to Clement; U.S. Pat. No. 5,562,803 to Wang; U.S. Pat. No. 5,755,926 to Hankins et al.; U.S. Pat. No. 6,010,593 to Tourtollet et al. and U.S. Pat. No. 6,019,872 to Kurle, the disclosures of which are hereby incorporated by reference.